C0 and C1 control codes (general category Cc)
- for compatibility with the nchar function,

Hangul Jamo medial vowels and final consonants
(code points with enumerable property UCHAR_HANGUL_SYLLABLE_TYPE
equal to U_HST_VOWEL_JAMO or U_HST_TRAILING_JAMO;
note that applying the NFC normalization with stri_trans_nfc
is encouraged),

ZERO WIDTH SPACE (U+200B),

Characters with the UCHAR_EAST_ASIAN_WIDTH enumerable property
equal to U_EA_FULLWIDTH or U_EA_WIDE are
of width 2.
SOFT HYPHEN (U+00AD) (for compatibility with nchar)
as well as any other characters have width 1.